Conventional mobile communications systems, particularly cellular systems, contain a number of base stations which communicate with mobile stations. If at least two base stations communicate simultaneously with the same mobile station, so-called macrodiversity transmission takes place. This mode of transmission is used, for example, in code division multiple access (CDMA) mobile communications systems. In the planned mobile communications system UMTS (universal mobile telecommunications system), macrodiversity transmission is to be used at least during handoff of the mobile station from one base station to another. In the UMTS, the powers transmitted by the base stations must be adapted as quickly as possible to changes in channel characteristics, which are caused by fading, for example. The mobile station sends to all base stations serving it a transmit power control (TPC) command instructing them to change their transmitted powers, namely to raise or lower the transmitted power level by a predetermined amount of, e.g., 1 dB.
The invention is predicated on recognition that the following problem arises if TPC commands are detected in error. If one of the base stations receives the TPC command incorrectly, it will change its transmitted power incorrectly as compared with those base stations which receive the TPC command correctly. This means that this individual base station will change its transmitted power in the opposite sense to the other base stations. Accordingly, the transmitted power levels will drift apart (xe2x80x9crandom walkxe2x80x9d). This drift reduces the desired macrodiversity gain. To prevent this drift, the invention proposes to preset for each base station an individual target value from which the transmitted power level should not deviate on a longterm average. Each base station changes its transmitted power in the direction of the target value assigned to it. Thus, in addition to the known power control loop, a further control loop is proposed which is traversed taking into account an externally preset target value. By this measure, a high macrodiversity gain is achieved even under poor receiving conditions. This second control loop can be traversed independently of the reception of the command.